The ultimate objective of this study is to elucidate more fully the nature of the cellular defects in blood and marrow in paroxysmal nocturnal hemoglobinuria (PNH) and to relate these to various in vivo and in vitro manifestations of PNH. Long-term studies on iron metabolism and the beneficial effects of androgen will be continued with emphasis on the mechanism by which androgen appears to lessen hemolysis in PNH. The basic mechanism of the diagnostic sucrose hemolysis test, described from this laboratory, will be studied with attempts to define the mechanism by which erythrocytes become coated with complement at low ionic strength. We have begun characterization of the erythrocyte acetylcholinesterase (AChE) in PNH cells. Initial work has pertained to differential effects of various membrane-solubilizing agents on AChE. Human red cell AChE has been purified 4200 fold and antibody made against it. Cytochemical characterization of AChE has been achieved in circulating red cells and marrow normoblasts in PNH with reference to the clonal hypothesis for PNH. Such studies will be extended to related blood dyscrasias. Since progressive hepatic venous thrombosis is a major threat in PNH, studies will be directed toward early detection and mechanisms with respect to liver scans, hepatic angiography, fibrin split products, and platelet function and cyclic AMP. The etiology of hemolytic transfusion reactions in PNH will be explored further with respect to leuko-agglutinins and circulating antiglobulins and immune complexes.